Metanefros

Metanefros, in languages that pluralize anatomical terms this way, refers to the metanephros, the final and functional stage of embryonic kidney development in jawed vertebrates. In amniotes—reptiles, birds, and mammals—the metanephros becomes the adult kidney. It develops after the earlier pronephros and mesonephros, which are transient embryonic kidneys in many vertebrates.

Development involves an interaction between two structures: the ureteric bud, which originates from the mesonephric duct, and the metanephric mesenchyme. The ureteric bud undergoes branching morphogenesis to form the collecting duct system, while the metanephric mesenchyme differentiates into nephron components, including the glomerulus, proximal tubule, loop of Henle, and distal tubule. Through these reciprocal interactions, the metanephros assembles the functional unit of the kidney.

Function and maturation follow a defined timeline. The metanephros becomes the organ responsible for urine formation and the regulation of fluid and electrolyte balance. In humans, kidney function begins during gestation, with continued maturation after birth.

Clinical and evolutionary notes help place the term in context. Disruptions in metanephric development can lead to congenital anomalies such as renal agenesis or hypoplasia. Evolutionarily, the metanephros is the kidney type characteristic of amniotes, whereas some non-amniote vertebrates rely more on mesonephric derivatives for their adult kidneys. Overall, metanefros denotes the plural usage of metanephros, the embryonic precursor that forms the mature kidney in many vertebrates.